Steady flow metering pump



1967 w. A. WILLIAMS 3,335,670

STEADY FLOW METERING PUMP Filed Jan. 25, 1965 4 Sheets-Sheet 1 g- 5 67 w. A, WILLIAMS 3,335,670

STEADY FLOW METERING PUMP Filed Jan. 25, 1965 4 Sheets-Sheet 2 W. A. WILLIAMS STEADY FLOW METERING PUMP Aug. 15, 1967 4 Sheets$heet 4 Filed Jan. 25, 1965 Expdnsidn bf Dischdrge Port In Cubic Units per Degree Degrees of Discharge Port Traverse By Roller Rate of Delivery of m f P 0 n .wfl r 0 h 0 C We 5 m m 0 m .1 8.5 d mD m R F.

H m 0 p 0 en r we Oh III-"C1 we. D m o '1 mf O R I 2 5 5 0 TO 8 p m u P q e WI 6 y MC F t x e N o 0 9 h c y C p m u P e n O United States Patent Office 3,335,670 Patented Aug. 15, 1967 3,335,670 STEADY FLOW METERING PUMP William A. Williams, Philadelphia, Pa., assignor to Milton Roy Company, St. Petersburg, Fla, a corporation of Pennsylvania Filed Jan. 25, 1965, Ser. No. 427,640 12 Claims. (Cl. 103-149) This invention relates to methods of and apparatus for producing, by the volume displacement principle, an accurately controlled flow of fluid which has for an object the production of a continuous flow of fluid at rates which may approach zero as a limit.

In the past, there have been available metering pumps of the volume-displacement type in two forms. The first involves a plunger moving into a metering chamber and which by the displacement of liquid produces a known discharge of such liquid. The second involves pumps of the peristaltic type. In pumps of the latter type, a liquid fills a flow channel either beneath a diaphragm which may be pressed downwardly into a flow channel to displace a volume of liquid ahead of a roller or the like, or it may comprise a deformable member such as a tube which is progressively pinched together by means of rollers likewise to displace a volume of liquid. In pumps or metering devices of both types, the output is characterized by its intermittent character. Though fairly uniform rates of flow have been obtained by utilizating two pumps with overlapping pumping cycles, nevertheless much has been left to be desired in obtaining a continuous flow, particularly with a single pumping device.

In carrying out the present invention in one form thereof, there has been utilized the principle of the peristaltic pump together with a unique configuration and contour of the outlet port which has heretofore caused an intermittent or variable rate of flow. In accordance with the present invention, there is maintained from one pumping cycle to another, a constant differential between the rate of delivery of fluid being transferred to the outlet port and the rate of change of the volume of the outlet port. More specifically, this is achieved by varying the width and depth of the pumping groove in the region of the outlet port thereby causing the pressure members to be disengaged from the pumping passage at a rate which produces a constant increase in volume of the pumping passage. The aforesaid rate of delivery of fluid to the outlet port is, of course, inherently constant. Contributing to the desired results is the equality provided between the length of the pumping passage in the region of the outlet port and the spacing between successive pairs of pressure members. This means that as one pressure member is leaving the region of the outlet port, another is entering it so that there is always compensation for the change in the volume of the pumping passage as each pressure member is gradually removed from it.

Metering devices or pumps presently in use which employ deformable fluid passages are often characterized by the fact that, after a period of use, the deformable fluid passage will suffer permanent deformation or lack of resiliency, thereby reducing the efliciency of the pump or metering device. In accordance with the present invention, these deficiencies of the prior art pumps or metering devices have been overcome by employing a flexible diaphragm around a grooved circumference of a drum together with a unique means for maintaining the flexible diaphragm in axial and circumferential tension by means independent of the elasticity of the diaphragm.

For further objects and advantages of the present invention, reference is to be had to the following description taken in conjunction with the drawings in which:

FIG. 1 is an exploded isometric view of the apparatus for effecting the present invention;

FIG. 2 is a sectional view taken on a plane suggested by line A-A of FIG. 1;

FIG. 3 is a sectional view taken on a plane suggested by line B-B of FIG. 1;

FIG. 4 is a developed view of the pumping groove;

FIG. 5 is a graph of the contour of the pumping groove at the outlet port;

FIG. 6- is a graph representing the constant rate of change of the volume of the discharge reservoir during one pumping cycle; and

FIG. 7 is a graph representing the constant rate of discharge of fluid from the discharge port through two pump cycles.

Referring now to the drawings, the invention in one form has been shown in FIG. 1 as applied to a volumetric metering device 1 supported by a frame 2. A motor 3 supported on the frame drives a gear reducer 4 from motor shaft 5. As best shown in FIG. 2, the output of the gear reducer appears at its output shaft 6 which is secured in driving relationship to support shaft 8 by set screw 38. Support shaft 8 is in its turn secured to the hub 7a of a driveplate 7 via set screw 39. The pump assembly 9 is journaled via bearing 37 on support shaft 8. Returning to FIG. 1, support bracket 10 secured as by screws 10a to the frame 2 serves to support the stationary part of the pump assembly 9, mounting screws 11 being provided for that purpose. The drive-plate 7 carries four rollers 12a12d, all four of which are shown in FIG. 3. Each roller is carried by a roller arm assembly 13, each having stub shafts 13a journaled in the peripheral portion of the driveplate 7. To each stub shaft 1311 there is secured one end of a spiral spring 15 with the opposite end engaging a stop pin 16 attached to the driveplate 7. The direction in which the spring 15 is wound is such as to bias the roller arm assembly 13 toward the support shaft 8. In the foregoing manner, all four rollers are biased downwardly against a diaphragm 14 disposed on the circumference of a drum 23. A groove 36 (FIG. 2) on the circumference of drum 23 forms a pumping passage 17 between the drum 23 and diaphragm 14. It is to be noted that in FIG. 1, all four rollers are shown in a retracted position so that the pump assembly 9 can be seen in greater detail. As will soon be described, the peristaltic element 14 is pressed inwardly progressively by rollers 1211-12d as they move around the circumference of the pump assembly 9 in the direction of the arrow shown on driveplate 7 of FIG. 1. In this manner, a peristaltic pumping action is generated whereby fluid is transferred from the inlet passage 21 around the circumference of the pump assembly 9 via pumping passage 17, FIG. 3 and discharged by way of the outlet passage 22.

Though the diaphragm 14 may be of any suitable flexible material, it is preferred that it be made of stainless steel, or of an alloy of beryllium, such as beryllium copper. It is a feature of the present invention that the diaphragm 14 be made of a two-part material, the outer, a metallic flexible material and the inner to be a laminate 14a lining, or coating of a reagent-resistant material such as KelF or Teflon, these materials being well known to those skilled in the art under their trade names such as fluoride materials of the polytetrafluorochloroethylene type or the polytetrafluoroethylene type. In order to further provide resistance to reagents as well as chemically active fluids of all kinds, the drum 23 which the diaphragm 14 surrounds may also be coated with or made of the same material as the laminate lining 14a as best seen in FIG. 2.

The manner in which the diaphragm 14 is wrapped about the drum 23 is best shown in FIGS. 2 and 3. Inasmuch as the metallic and plastic coated diaphragm 14 is to be pressed inwardly of the drum 23 progressively 3 to close the pumping passage 17, there are provided flexible mounting means for the diaphragm 14. Though, it can flex to some degree, it is nevertheless important to keep the pumping diaphragm 14 both in circumferential and axial tension. Accordingly, an important feature of the present invention resides in the provision (FIG. 2) of two circular clamping rings 18, 18a, one of each being disposed adjacent the respective ends of the drum 23. These semi-circular clamping rings 18, 18a are provided with serrated inner surfaces 24 and are tightly clamped downwardly against the diaphragm 14 to press it in fluidtight relationship with the outer surface of the drum 23, the clamping screws 25 shown in FIG. 1 being supplied for this purpose. The serrations or teeth 24 provided in the clamping rings 18, 18a dig into the diaphragm 14 thereby rigidly securing the clamping rings 18 and 18a. in secure relationship to the metallic diaphragm 14.

Axial tension is developed by concave disc-like spring elements 19 known in the art as Belleville springs. These disc-like elements engage hub portions 26 and 26a of drum 23. Through the peripheral portions of spring elements 19, there extends a plurality of screws 20 which are uniformly tightened around the circumference of the spring elements 19. Thus, depending upon the torque applied to the plurality of screws 20, the Belleville springs 19 will exert outwardly directed tensile forces upon the clamping rings 18 and 18a which in turn act to maintain the diaphragm 14 in axial tension upon drum 23.

The diaphragm 14 is maintained in circumferential tension by a tightening and clamping assembly best shown in FIG. 3. The ends of diaphragm 14 pass into an axially extending slot 29 and are secured between diaphragm clamping bars 30 and 31 which extend the full width of diaphragm 14. The clamping bars 30 and 31 are secured to each other and to the ends of diaphragm 14 by means (not shown) such as screws which pass through an opening in clamping bar 30- and thread into clamping bar 31. Upon selectively tightening screws 32 (only one shown), a selected circumferential tension is established on diaphragm 14. To assure operation under the circumferential tension, the clamping bar 31 never rests against the bottom of slot 29.

Bridge member 44 shown in FIG. 3 is positioned across the slot 29 in order that the rollers 12a-12d may pass thereover. The bridge member 44 is secured in place at its ends adjacent the respective ends of drum 23 by the clamping rings 18 and 18a. That is, said ends of the bridge member are positioned underneath rings 18 and 18a so that when the clamping rings are tightened upon the circumference of drum 23, the bridge member 44 will accordingly be drawn into securing engagement with the drum 23.

The details of the discharge port 28 can best be seen by reference to FIGS. 2, 3 and 4. It includes a discharge reservoir 42 (best shown in FIG. 2) formed by a sawcut extending radially into drum 16. The discharge passageway 43 extends from the discharge reservoir 42, and connects with the outlet passage 22 (-best shown in FIG. 1). The depth of the pumping passage 17 can be seen in both FIGS. 3 and 4 to diminish from its maximum depth at the leading edge 47 of discharge reservoir 42, to zero depth at the trailing edge 48 of the discharge reservoir 42.

The rollers themselves may be provided with a core portion 33 of any suitable material and an outer peripheral portion 34 which is preferably made of a deformable material, such as a synthetic rubber. The rollers are provided with a crowned surface 35 (best shown in FIG. 2), or in other words, curved or toroidal surfaces with the higher part midway of the ends of the roller.

The operation of the metering device of the present invention can best be seen with reference to FIGS. 3-7. As a given roller passes over and beyond the intake port 27, fluid will be displaced in front of the roller. As the diaphragm 14 returns to its original position, the resultant suction causes fluid to be drawn into the pumping passage A 17 from chordal intake reservoir 40 and intake passageway 41.

As the rollers continue to revolve around the circumference of the drum 23, the fluid in front of the rollers will be transferred accordingly in the direction of the discharge port 28. Upon a given roller, roller 12a in FIG. 3, reaching the leading edge 47 of the discharge port 28,'the roller 12a will cease its pumping function since in the region of the discharge reservoir 42, there is a fluid connection to both sides of the roller 12a. However, at the very moment it ceases its pumping action, the next following roller, 12d in FIG. 3, takes over the pumping function and continues the delivery of fluid through the passages 22 and 43.

It will be noted that roller 12a, although serving no pumping function after passing leading edge 47, nevertheless occupies a portion of the volume of discharge reservoir 42, particularly, a volume like that indicated at 49 underneath the diaphragm 14 as depressed by roller 12a. The rollers must return to the top of the pumping passage 17 preparatory to their next pumping cycle. It will be appreciated that if the roller 12a were to be suddenly disengaged from the pumping passage, as is characteristic of metering devices employing the peristaltic principle as heretofore known, the volume of the discharge reservoir 42 would abruptly increase and hence cause a pulse in the output by a momentary decrease in flow.

The peristaltic pump of the present invention eliminates such a pulse in the output by effecting the disengagement of the rollers through a distance equal to that between two adjacent rollers and at a rate which maintains constant the rate of change of volume of the discharge reservoir during such disengagement of the rollers.

It will be noted that as the depth of the pumping passage diminishes from a maximum depth at the leading edge 47 to zero at the trailing edge 48 of the discharge port 28, its cross-sectional area also diminishes (see FIG. 4). Thus, in order to maintain a constant rate of change of volume of discharge reservoir 42 as roller 12a is disengaged from diaphragm 14 in travelling the extent of the discharge port, the rate of disengagement is increased as the cross-sectional area decreases. This rate of increase of disengagement can be derived by mathematical analysis or experimentation for any given set of conditions such as, among other things, the pumping passage, depth and width, distance between two adjacent rollers and the radius of curvature of the crown of the rollers.

FIG. 5 shows the specific rate of disengagement or function for producing a constant rate of change of volume of discharge reservoir 42 in one exemplary embodiment disclosed wherein the maximum depth of the pumping groove was .008 and the angle between two adjacent rollers FIG. 6 illustrates the constant rate of the expansion of the discharge reservoir 42 in terms of cubic units per degree of discharge port traversed by a given roller.

Now, following the operation of the pump of the present invention through a complete discharge cycle, it will be observed that, as roller 12d is driven towards the discharge port 28 at a constant speed, the fluid between roller 12d and roller 12a is forced along in front of roller 12d at a constant rate also. It will also be observed that, as roller 12a also progresses toward the trailing edge 48 of discharge port 28, the volume of discharge reservoir 42 will be increasing at a constant rate. Thus, for the cycle being considered, the fluid between roller 12d and roller 12a will be discharged into a reservoir whose volume is being increased at a constant rate. However, the volume of discharge in front of roller 12d is greater than the rate at which the discharge reservoir 42 is increasing. Thus, there will be a discharge from'the discharge port 28 which is the differential between the constant rate of delivery to discharge reservoir 42 and the constant rate of expansion of discharge reservoir 42.

This can be seen in FIG. 7 where, for a given discharge cycle represented by 0 to 90, line 52 represents the uniform rate of expansion in cubic units per degree of the discharge reservoir 42, and line 51 represents the uniform rate of delivery of fluid in front of roller 12d in cubic units per degree. Thus, it can be seen as both rates are uniform, both lines will be parallel to the abscissa of the graph. The distance between lines 51 and 52 represents the differential between the rate of delivery to the discharge reservoir 42 and the rate of expansion of discharge reservoir 42 and consequently the rate of discharge from discharge port 28. As both lines 51 and 52 are parallel between the limit O-90 which represents one pump cycle, it will be appreciated that the rate of discharge must be constant throughout the cycle. The area between lines 51 and 52 for the interval of 0-90 will represent the volume of discharge for a given cycle.

Referring again to FIG. 3, it will be noted that as one roller, namely 12b, has completed its cycle of climb-out, asecond roller, in this case 12a, is just beginning its cycle of climb-out. This is because the angle subtended by two given rollers is equal to the angle subtended by the discharge reservoir 42.

Thus, there is always a smooth transition from one pumping cycle to the next, since from cycle to cycle the rate of flow into the discharge reservoir 42 remains constant, as well as the rate of expansion of discharge reservoir 42 as seen by each roller in its turn. In this manner, the rollers may be sequentially disengaged from the pumping passage 17 while the resultant differential which represents the rate of output of the peristaltic pump of the present invention will be a constant rate of flow throughout the transition from one cycle to another. This is also shown in FIG. 7 where lines 51 and 52 can be seen to extend horizontally and without interruption from one cycle to another through the transition points represented at 90 and 180. Thus, any number of rollers and any spacing therebetween may be used so long as the spacing is uniform and equal to the length of the discharge reservoir over Which disengagement of the rollers occurs.

Conditions may require that a pump have a uniform and constant intake suction as well as a uniform and constant discharge, or even a uniform and constant intake suction alone. It will be appreciated that the inventive concept utilized in the discharge port of the present invention can be employed in the intake port 27. In such a case, the rate of volumetric intake would be the differential of the rate of volume generated as the diaphragm 14 returns to its normal position upon a roller passing, and the rate at which the adjacent following roller decreases the volume of the intake reservoir 40. The intake port 27 would of course, in the embodiment disclosed, subtend an angle equal to that between two adjacent rollers or 90.

In the embodiment of the invention disclosed, the drum 23 was made two inches in diameter; the maximum depth and width of the pumping passage 17 were .008" and .625 respectively, the radius of the groove 36 was 12 inches, and the rollers 12a12d revolved around the axis of drum 23 at approximately twenty revolutions per minute. This resulted in an extremely accurate, uniform and non-pulsating flow at the discharge of the pump of 1 cc./

It is of course to be understood that the above-referred to dimensions are not to be in any respect limiting of the invention hereinbefore disclosed.

It is expected that the dimensions of the above-disclosed pump may be altered as desired to increase or decrease the flow. Further, the motor speed can be changed to accordingly vary the flow rate as may be desired.

While there has been a specific embodiment of the present invention discussed, it will be evident to one skilled in the art that various changes may be made in the ap- 6 paratus without departing from the scope of the invention as set forth in the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is 1. A peristaltic metering pump comprising:

means defining a flow passage for fluid to be pumped,

transfer means providing an inlet passage to said flow passage,

transfer means providing an outlet passage from said flow passage,

means for progressively applying a pumping force to said flow passage to move fluid along said flow passage, and

means for maintaining a constant differential between the rate of transfer of fluid being pumped in the region of said transfer means and the rate of volum etric change of the portion of said flow passage in said region, whereby there is achieved a continuous non-pulsatin g flow of said fluid.

2. A peristaltic metering pump comprising:

means defining a flow passage for fluid to be pumped,

inlet means providing an inlet passage for said fluid to said means defining said flow passage,

outlet means providing an outlet for said fluid from said means defining said flow passage,

means for imparting a uniform and cyclic peristaltic pumping action to said fluid in said means defining said flow passage, and

means for maintaining, from one peristaltic pumping cycle to another, a constant differential between the rate of delivery of fluid being pumped to the region of said outlet means and the rate of volumetric change of the portion of said means defining said flow passage in said region due to the transition from one peristaltic pumping cycle to another, whereby a continuous non-pulsating flow of said fluid being pumped will be discharged from said outlet means.

3. In a peristaltic metering pump having a flexible fluid passage and a plurality of uniformly spaced pressure members which sequentially pass into closing engagement with said fluid passage at a first point and transfer therealong fluid to a second point at which said pressure members are disengaged from said fluid passage, the method of maintaining a uniform flow of fluid discharged from said fluid passage which comprises:

effecting the disengagement of said plurality of pressure members over a distance equal to that between two adjacent pressure members and at a rate which will maintain constant the rate of change of volume of said fluid passage resulting from said disengagement.

4. In a peristaltic metering pump having a flexible fluid passage and a plurality of uniformly spaced pressure members which sequentially engage said fluid passage at an intake port and sequentially pass along said flexible fluid passage thereby transferring fluid to a discharge port where said plurality of pressure members are sequentially disengaged from said flexible conduit, the method of maintaining a uniform discharge of fluid at said port from one cycle to another which comprises:

starting disengagement of a given pressure member at the time it reaches said discharge port and effecting said disengagement over a distance equal to the distance between two adjacent pressure members and at an incremental rate which will maintain constant the rate of change of volume of said flexible fluid passage resulting from said disengagement.

5. In a metering pump of the positive displacement type in which each of a plurality of lengths of a flow channel are filled with liquid forming discrete trapped volumes therealong, the method of producing and maintaining a uniform flow of fluid at an outlet passage of said metering pump comprising:

moving said discrete volumes of liquid along said passage toward said outlet,

transferring the flow of fluid to said outlet passage from one trapped volume to the next in the region of said outlet passage, and

in said region of said outlet passage and over a length equal to the length of each said trapped volume, increasing the volume of the passage, said volumetric increase being linear and equal for each incremental decrease in the length of one of said trapped volumes in said region of transfer, whereby there is achieved said uniform flow.

6. The method of producing and maintaining a uniform flow of fluid discharged from the outlet passage of a metering pump which comprises:

successively filling each of a plurality of equal-lengths of flow channel located between equally space-d pumping elements,

moving said elements along said channel for positive displacement along said channel of the fluid trapped between said elements,

in the region of said outlet passage in communication with said channel, transferring the flow of fluid ahead of one element to the fluid being displaced by the preceding element, and

in said region of said outlet passage and over a length equal to the distance between said elements first by one and then by each succeeding element, increasing the volume of the passage, said volumetric increase being linear and equal for equal incremental displacements of the pumping element occupying said region of transfer, whereby there is achieved said uniform flow.

7. A metering pump comprising:

flexible conduit means defining a flow passage for fluid to be pumped,

inlet means providing an inlet passage for fluid to said flexible conduit means,

outlet means providing an outlet for fluid from said flexible conduit means,

a plurality of pressure members uniformly spaced one from the other,

means supporting said plurality of pressure members to uniformly and sequentially bring said plurality of pressure members into closing engagement with said flexible conduit means at said inlet means, to move said pressure members along said flexible conduit means and to disengage said pressure members from said flexible conduit means at said outlet means, whereby fluid will be drawn into said flexible conduit means at said inlet means, displaced along said flexible conduit means between adjacent pressure members, and discharged from said flexible conduit means at said outlet means,

means for \(a) starting said disengagement of a given pressure member from said flexible conduit at the time said given pressure member reaches said outlet means and consequently ceases to transfer liquid, and

(b) effecting said disengagement over a distance equal to the distance between two adjacent pressure members at an incremental rate which will maintain constant the rate of change of volume of said flexible conduit means resulting from said disengagement, thereby maintaining the rate of discharge of fluid from said outlet means constant and non-pulsating throughout the sequential transfer of fluid by said plurality of pressure members.

8. A peristaltic metering pump comprising:

a drum,

a pumping groove formed in and around a portion of the circumference of said drum,

a flexible diaphragm disposed around said circumference of said drum and overlaying said pumping groove, thereby forming a flexible fluid passage on the circumference of said drum between said diaphragm and said drum,

transfer means providing an inlet passage to said fluid passage,

transfer means providing an outlet passage from said fluid passage,

means for progressively applying a pumping force to said fluid passage to move fluid along said fluid passage,

an axial slot in the circumference of said drum and extending inwardly toward the center thereof to a depth below that of the pumping groove, and

means disposed within said slot and below said pumping groove for maintaining said flexible diaphragm in circumferential tension by gripping either end thereof and urging said ends inwardly toward the center of said drum.

9. The peristaltic metering pump of claim 8 further including a bridge member disposed across said axial slot providing said drum with smooth outer contour for smooth passage thereover by said means for progrssively applying the pumping force to the fluid passage.

10. A metering pump comprising:

a drum having a pumping groove formed on a portion of the circumference thereof,

a flexible diaphragm disposed on a portion of said circumference of said drum at least coextensive with said pumping groove to thereby form a flexible fluid passage on said circumference of said drum,

means for securing said diaphargm in fluid-tight rela tionship about said drum,

inlet means providing an inlet passage for fluid to said fluid passage,

outlet means providing an outlet passage for fluid from said fluid passage,

said inlet means and said outlet means being located at opposite ends of said fluid passage,

a plurality of pressure members uniformly spaced one from the other,

means for supporting said plurality of pressure members uniformly and sequentially to bring them into closing engagement with said fluid passage at said inlet means,

means for moving said pressure members along said fluid passage and to disengage said pressure members from said fluid passage at said outlet means, whereby fluid is drawn into said fluid passage at said inlet means, displaced along said fluid passage between adjacent pressure members, and discharged from said fluid passage at said outlet means,

means for maintaining said flexible diaphragm in axial and circumferential tension, and

means for starting said disengagement of a given pressure member from said fluid passage at the time said given pressure member reaches said outlet means thereby ceasing to transfer liquid; and effecting said disengagement over a distance equal to the distance between two adjacent pressure members at an incremental rate which will maintain constant the rate of change of volume of said flexible fluid passage resulting from said disengagement, thereby maintaining the rate of discharge of fluid from said outlet means constant and nonpulsating throughout the sequential transfer of fluid by said plurality of pressure members.

11. A peristaltic metering pump comprising:

a drum,

a pumping groove formed into and around a portion of the circumference of said drum in a plane perpendicular to the axis of said drum and midway between the ends thereof,

a flexible diaphragm disposed around said circumference of said drum and overlying said pumping groove, thereby forming a flexible fluid passage on said circumference of said drum between said diaphragm and said drum,

inlet means providing an inlet passage for fluid to said fluid passage,

outlet means providing an outlet passage for fluid from said fluid passage,

said inlet means and said outlet means located at opposite ends of said fluid passage,

a plurality of deformable rollers uniformly spaced one from the other around the circumference of said drum in said plane and in forceful engagement with said diaphragm on said circumference of said drum,

means supporting said plurality of deformable rollers for revolution around said axis of said drum in a direction from said inlet means to said outlet means, whereby fluid will be drawn into said fluid passage, displaced along said fluid passage between adjacent rollers and discharged from said fluid passage at said outlet,

means disposed intermediate the ends of said drum for drawing and maintaining said flexible diaphragm in circumferential tension on said drum,

clamping means positioned circumferentially of said diaphragm at either end of said drum and disposed in clamping engagement with said diaphragm, and

spring means supported adjacent each of said clamping means and connected thereto for urging said clamping means axially apart thereby drawing and maintaining said diaphragm in axial tension.

12. The peristaltic metering pump of claim 11 wherein said outlet means includes a discharge port having a leading and trailing edge and subtending an angle equal to the angle between two adjacent rollers, and

said pumping groove extending on the circumference of said drum through said subtended angle and the depth thereof diminishing from a maximum at the leading edge of said port to zero at the trailing edge of said port according to a prescribed function which will maintain constant the rate of increase of volume of said fluid passage as a given roller is disengaged from said fluid passage upon movement from the leading edge of said port to the trailing edge thereof, whereby a constant and nonpulsating delivery of fluid from said port will result upon revolution of said rollers around the axis of said drum.

References Cited UNITED STATES PATENTS 813,443 2/ 1906 Mikorey 230168 2,987,005 6/1961 Dann 1U3149 3,007,419 11/ 1961 Burt 103-223 FOREIGN PATENTS 57,423 1/ 3 France. 484,479 5/ 1938 Great Britain.

DONLEY I. STOCKING, Primary Examiner.

W. L. FREEH, Assistant Examiner. 

1. A PERISTALIC METERING PUMP COMPRISING: MEANS DEFINING A FLOW PASSAGE OF FLUID TO BE PUMPED, TRANSFER MEANS PROVIDING AN INLET PASSAGE TO SAID FLOW PASSAGE, TRANSFER MEANS PROVIDING AN OUTLET PASSAGE FROM SAID FLOW PASSAGE, MEANS FOR PROGRESSIVELY APPLYING A PUMPING FORCE TO SAID FLOW PASSAGE TO MOVE FLUID ALONG SAID FLOW PASSAGE, AND MEANS FOR MAINTAINING A CONSTANT DIFFERENTIAL BETWEEN THE RATE OF TRANSFER OF FLUID BEING PUMPED IN THE REGION OF SAID TRANSFER MEANS AND THE RATE OF VOLUMETIC CHANGE OF THE PORTION OF SAID FLOW PASSAGE IN SAID REGION, WHEREBY THERE IS ACHIEVED A CONTINUOUS NON-PULSATING FLOW OF SAID FLUID. 